Two of the priority research areas identified by the NIH Bioengineering Nanotechnology Initiative are Nanoimaging and Molecular and Cellular Sensing/Signaling. This proposal presents SERS nanotags (SERS = Surface Enhanced Raman Scattering), a new detection technology, which will enable the rapid and quantitative measurement of many chemical species both in solution and under a microscope. We propose to synthesize, fully characterize, and demonstrate initial bioassay results using these glass-coated nanoparticulate optical tags based on SERS. Our specific aims for this proposal are: 1. Prepare a set of five or more SERS tags with clearly different spectra. We will synthesize Au and Ag nanoparticles that provide SERS enhancement, show that molecules with five different spectra can be readily combined with the particles, and coat them with a controlled amount of glass. 2. Examine the ability of SERS nanotags to function as quantitation tags. This will include a determination of the signal generated per particle and a demonstration of the ability to extract accurate quantitative information from mixtures of particles. 3. Demonstrate ability to use SERS nanotags in a bioassay. To achieve this aim we will first show the attachment of biomolecules (specifically streptavidin and oligonucleotides) to the glass-coated SERS nanotags. Finally, we will carry out a competitive binding assay between biotin and desthiobiotin to show that the SERS nanotags can provide quantitative data in a bioassay format. The attainment of these aims will establish the foundation for unprecedented capabilities in optical tag-based localization and quantitation, with applications ranging from multiplexed gene expression analysis to multiplexed histopathogical analysis of cancerous tissue. SERS is the 10(6)- to 10(14)-fold enhancement in Raman scattering obtained from molecules in extremely close proximity to nanoscale-roughened noble metal surfaces. This enhancement is necessary in order to use Raman scattering as a sensitive tagging technique for bioassays.